1. Field of the Invention
The present invention is generally related to a method of making 6-aminocaproic acid, and more particularly to a method of making 6-aminocaproic acid as an active pharmaceutical ingredient.
2. Description of the Prior Art
At present, various methods of making 6-aminocaproic acid are known and established because of its extensive applications. 6-aminocaproic acid is used in industry as a starting material for polymerizing ε-caprolactam to form Nylon-6 while medically it can be used to treat bleeding. However, 6-aminocaproic acid as an active pharmaceutical ingredient requires properties such as low ash content (i.e. low salt content or low residue on ignition), low heavy metal content, low water content, and no foul odor in addition to high purity. Besides, the processes of making 6-aminocaproic acid also require no involvement of toxic materials.
The method of making 6-aminocaproic acid, according to the prior art, includes the methods disclosed in Organic Syntheses, Coll. Vol. 4, p. 39 (1963) and Vol. 32, p. 13 (1952) where ε-caprolactam was hydrolyzed and then purified by column chromatography using Amberlite resin. However, the purification by ion exchange resin causes the product containment with colored impurity and odor. This method usually used to produce small amount of products and associated with high cost. It is not practical to use in large scale production.
On the other hand, U.S. Pat. No. 3,655,748 disclosed a method of making 6-aminocaproic acid from ε-caprolactam. Although it was reported that the produced 6-aminocaproic acid was obtained with low ash content, the process includes mixing ε-caprolactam with barium hydroxide, hydrolyzing ε-caprolactam to produce 6-aminocaproic acid, adding CO2 gas to form precipitates of barium carbonate to obtain free acid of 6-aminocaproic acid. However, barium carbonate is toxic and is not suitable for the active pharmaceutical ingredient application.
The other methods, for example, reported in U.S. Pat. No. 4,950,429, U.S. Pat. No. 6,452,002, U.S. Pat. No. 6,372,939, for making 6-aminocaproic acid are mostly applied to Nylon-6 production and have problems for the active pharmaceutical ingredient application, such as complicate processing, expensive reagents, toxic intermediates, and high ash content.
Therefore, a novel method of making 6-aminocaproic acid (or ε-aminocaproic acid) as an active pharmaceutical ingredient is urgently needed to produce high quality product to meet medical requirements.